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16th CENTURY NAVIGATION TOOLS

During the Age of Discovery methods of navigation developed quickly because of the need of European explorers venturing to the New World discovered by Columbus in 1492. The instruments navigators used varied and included the quadrant, astrolabe, cross staff, hourglass, compass, map or nautical chart, and other devices.

THE COMPASS
The compass was known to be in China as early as the 3rd century B.C. It was not in use in Europe until about the 12th century and was common by the 15th century. The compass did not have degrees marked on it like present-day compasses. Compasses used in the 15th-16th centuries displayed the 32 points of direction known as a compass rose. The points of direction were usually 11.25 degrees apart, indicating north, north by east, north by northeast, etc. The magnetic compass during the Age of Discovery was typically composed of a magnetized metal needle attached to a compass rose by a brass pin so the needle would swing freely. It was then hung by gimbals, which are concentric mounting rings that allowed the compass to remain relatively level during travel, and it was kept in a wood box. One component of the compass was a piece of magnetic iron ore or lodestone, used to re-magnetize the compass needle as needed. These navigation instruments were magnetic so the needle pointed to magnetic north not true north. Navigators found variations of magnetic north depending on your location. So they had to account for this variation when they traveled to different parts of the world. Christopher Columbus reported the variations of true north and magnetic north during his voyages across the Atlantic Ocean. The compass could be used in all weather, day or night. It was not dependent on clear weather for use like other navigation instruments such as the astrolabe or quadrant.

QUADRANT
The quadrant was a celestial navigation tool used to find latitude. It was a quarter panel of wood or brass with degrees marked on the outer edge of the arch, a plumb line, and sight along one edge. The instrument was used to measure the altitude of the star Polaris. The reading was taken where the plumb line intersected the degree on the outer edge of the arch.

ASTROLABE
Like the quadrant, the astrolabe was used to find latitude. It was a circle made of brass or wood with degrees on the edges and a moveable alidade or sighting arm. It could be used at night to sight in on Polaris to obtain the latitude. If the alidade had a sight with pinholes on either end, it could be used during the day by measuring the sun. The astrolabe was used by holding from the ring at the top and the sight moved until the sun shined through the pinholes. The degree was then read. If used at night, it was held by the ring with one hand, the other hand moved the alidade until it was sighted in on Polaris. Then the degree was read. Sometimes the astrolabe was by a pair of sailors, one to sight and the other to steady the device and take the reading.

HOURGLASS
The hourglass was the most common means for counting tie at sea. These were usually four-hour size and a half -hour size. The hourglass consists of two glass bulbs place one on top of the other and connected by a narrow tube. One bulb is filled with sand which flows through the tube into the bottom bulb at a given rate. Once the sand fills the bottom bulb, it can be turned over and time started again.

The hourglass was used to measure the day at sea which was divided into six four-hour watches. At the end of the four hours, the glass was turned for a new watch. In conjunction with the four-hour glass, a half-hour glass was also used. At the end on a half-hour, the glass was turned and the bell rang. One of the ship’s boys was usually responsible for watching and taking care of the hourglasses.

Another use of the hourglass was with the log or chip line used to determine the speed of the ship. A piece of wood was attached to a line that had been knotted at regular intervals. From the stern, a mariner would toss the log into the water and let the line flow freely. When he felt the first knot pass through his hands, he shouted a sailor who turned a thirty-second glass or a one-minute glass. The person holding the line would then count out loud the number of knots that passed through his hand in thirty seconds or one minute. A simple math formula was used to determine the nautical miles per hour of the ship. One calculation gives the speed of “one knot or nautical mile” as equal to about 1.151 miles per hour. The speed is also known as “knots” which is a term still used by mariners today.

OTHER INSTRUMENTS
Other navigation devices that were in use in the 16th century included the cross staff, used to measure a celestial body over the horizon; the back staff used to sight in on the sun; and the traverse board for keeping track of changes in course and speed of the ship (though used in the 16th century, it was more common in the 17th century).